The present invention relates to optical switches. More particularly, the present invention relates to insulation for improving the thermal efficiency of a bubble optical switch.
One type of optical switch is based on inkjet printer technology and planar lightwave circuit technology. These optical switches route an optical stream from one path to another without having to convert the signal from optical, to electronic, and back to optical. Instead, these optical switches use bubbles, which are formed by vaporizing the fluid in the optical switch, to switch light signals from one optical fiber to another. The optical switches have a planar lightwave circuit, which includes a grid of intersecting paths or waveguides, mounted on a matrix controller substrate. At a cross point of two waveguides is a trench filled with fluid that has the same optical properties as the glass in the waveguides. As a result, light or an optical stream and its communications contents can travel unimpeded through the cross point.
When the optical signal needs to be rerouted, a bubble heater warms the appropriate trench to insert a vapor bubble at the cross point. The vapor bubble alters the optical properties of the cross point, thereby causing the light to be reflected along a different path. The bubbles can be formed and removed hundreds of times per second, providing a fast and reliable switching function, one without the use of mirrors or other mechanical moving parts.
This type of optical switch has a core, which includes the bubble heaters and the planar lightwave circuit, and a fluid reservoir. The fluid reservoir supplies the fluid to the trenches in the planar lightwave circuit. The optical switch can form a bubble and set up a switch path in under 10 milliseconds. In order for the optical switch to quickly switch among optical paths, the fluid reservoir must be kept a temperature higher than that of the core of the switch. The optical switch includes thermoelectric coolers, which ensure that the core of the switch is maintained at a lower temperature than the fluid reservoir. The thermoelectric coolers remove heat from the core of the optical switch and pump a portion of that heat to the fluid reservoir.
One problem with this type of optical switch is that thermal leakage occurs between the fluid reservoir and the core of the optical switch, with heat from the fluid reservoir leaking into the core. This thermal leakage causes the thermoelectric coolers to work harder, as the thermoelectric coolers must remove the heat that has leaked from the fluid reservoir, in addition to the heat that is generated by the electronic circuitry in the core. The additional work of the thermal electric coolers creates more heat, which also must be dissipated. The amount of heat that the optical switch must dissipate affects the size of the heat sink and ultimately, the size of the switch. Thus, it would be desirable to minimize the amount of thermal leakage between the fluid reservoir and the core of the optical switch.
Another problem present in this type of optical switch is the thermal gradient of the planar lightwave circuit. The bottom surface of the planar lightwave circuit is closer to the bubble heaters of the matrix controller substrate than the top surface where the bubbles are formed in the trenches. Thus, there is some heat loss at the top surface of the planar lightwave circuit. Variation in temperature across the planar lightwave circuit can adversely affect operation of the optical switch. Thus, it is desirable to provide an optical switch with a planar lightwave circuit that has both a more uniform temperature profile and a more stable temperature.
Still another problem with these optical switches is the accumulation over time of atmospheric gases in the fluid of the optical switch. Because the optical switch uses vapor bubbles rather than air bubbles, a substantial accumulation of atmospheric gases can affect performance of the optical switch. There is a need, therefore, for an optical switch that is better insulated from the seepage of atmospheric gases into the optical switch.
In accordance with one embodiment of the present invention, an optical switch includes a core, a fluid reservoir and a thermal solution. The core includes a base, a matrix controller substrate mounted on the base, and a planar lightwave circuit. The planar lightwave circuit has a plurality of waveguides and a plurality of trenches. Each trench is located at an intersection of two waveguides. The fluid reservoir contains a fluid, which the reservoir supplies via a tube to the plurality of trenches of the core. The core and the fluid reservoir are mounted on the thermal solution. The thermal solution maintains the fluid reservoir at a higher temperature than the core, by removing heat from the core and transferring at least a portion of the heat to the fluid reservoir. The optical switch further includes an insulating structure that covers the core and the fluid reservoir. The insulating structure prevents thermal leakage from the fluid reservoir to the core and improves the temperature profile of the planar lightwave circuit. In addition, the insulating structure can prevent atmospheric gases from seeping into the optical switch. Materials used in the insulating structure include aerogels and xerogels.
In accordance with another embodiment of the present invention, a method of making an optical switch includes providing an optical switch having a core, a fluid reservoir coupled to the core via a tube, and a thermal solution. The optical switch has the features described above. The method further includes providing a clam-shell device having a top half and a bottom half, and placing a first membrane in the top half of the clam-shell device and a second membrane in the bottom half. The first and second membranes are then filled with an insulating material, and the optical switch is placed in the clam-shell device. The clam-shell device is then closed on the optical switch, and the first and second membranes containing the insulating material are vacuum formed about the optical switch. The first membrane covers an upper surface of the core, the fluid reservoir and the tube, and the second membrane extends along a bottom of the tube and covers an area between the core and the fluid reservoir. The first and second membranes that are filled with the insulating material reduce a thermal leakage between the fluid reservoir and the core and improve the temperature profile of the planar lightwave circuit of the core.
In accordance with still another embodiment of the present invention, a method of making an optical switch includes providing an optical switch and surrounding the core, the tube and the fluid reservoir of the optical switch with a membrane. The method further includes filling the membrane with an insulating material and applying a vacuum and sealing the core, the tube, the fluid reservoir and the insulating material in the membrane. The membrane can be made of an aluminum or polymeric film, and the insulating material can include aerogels and xerogels. The insulating material isolates the fluid reservoir from the core to minimize heat loss from the fluid reservoir as well as to improve the temperature profile of the planar lightwave circuit. In addition, the vacuum-sealed membrane and insulating material prevent unwanted atmospheric gases from entering the optical switch.